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Message-ID: <20160628004718.GS25646@wotan.suse.de>
Date: Tue, 28 Jun 2016 02:47:18 +0200
From: "Luis R. Rodriguez" <mcgrof@...nel.org>
To: Andi Kleen <andi@...stfloor.org>
Cc: "Luis R. Rodriguez" <mcgrof@...nel.org>,
"H. Peter Anvin" <hpa@...or.com>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
X86 ML <x86@...nel.org>, Borislav Petkov <bp@...en8.de>,
Andy Lutomirski <luto@...capital.net>
Subject: Re: Is LTO_REFERENCE_INITCALL() still needed?
On Fri, Jun 24, 2016 at 02:07:53PM -0700, Andi Kleen wrote:
> > But nothing quite obviously setting these upstream. I'm probably just
> > missing something obvious though. Either way I figured now would be a
> > good time to ask as I have other code that would use this, the linker
> > table stuff I've been working. If we can avoid propagating more use of
> > LTO_REFERENCE_INITCALL() then great. If we still need it its probably
> > good to document this a bit more as can't see anything super clear.
>
> It was a work around for a gcc 4.7 LTO problem. I guess it could be
> dropped by now.
>
> Yes I've been slow in submitting the LTO patches, even though they
> have a quite active out of tree user base. Will try to do better.
Would something like this make sense then? Tested by 0-day.
>From 682579b548ccf5d33349f32fcbe0922f5c29f04d Mon Sep 17 00:00:00 2001
From: "Luis R. Rodriguez" <mcgrof@...nel.org>
Date: Mon, 27 Jun 2016 14:25:14 -0700
Subject: [PATCH] x86: remove LTO flags
The setup for LTO never made it upstream, and although this has
some users, this is now really old stuff for a gcc 4.7 LTO problem.
Signed-off-by: Luis R. Rodriguez <mcgrof@...nel.org>
---
arch/x86/entry/vdso/Makefile | 6 ++----
include/linux/init.h | 20 +-------------------
kernel/Makefile | 3 ---
scripts/Makefile.build | 2 +-
4 files changed, 4 insertions(+), 27 deletions(-)
diff --git a/arch/x86/entry/vdso/Makefile b/arch/x86/entry/vdso/Makefile
index 3288dfa63706..d0f1cd210892 100644
--- a/arch/x86/entry/vdso/Makefile
+++ b/arch/x86/entry/vdso/Makefile
@@ -2,7 +2,6 @@
# Building vDSO images for x86.
#
-KBUILD_CFLAGS += $(DISABLE_LTO)
KASAN_SANITIZE := n
UBSAN_SANITIZE := n
OBJECT_FILES_NON_STANDARD := y
@@ -49,8 +48,7 @@ export CPPFLAGS_vdso.lds += -P -C
VDSO_LDFLAGS_vdso.lds = -m64 -Wl,-soname=linux-vdso.so.1 \
-Wl,--no-undefined \
- -Wl,-z,max-page-size=4096 -Wl,-z,common-page-size=4096 \
- $(DISABLE_LTO)
+ -Wl,-z,max-page-size=4096 -Wl,-z,common-page-size=4096
$(obj)/vdso64.so.dbg: $(src)/vdso.lds $(vobjs) FORCE
$(call if_changed,vdso)
@@ -171,7 +169,7 @@ quiet_cmd_vdso = VDSO $@
sh $(srctree)/$(src)/checkundef.sh '$(NM)' '$@'
VDSO_LDFLAGS = -fPIC -shared $(call cc-ldoption, -Wl$(comma)--hash-style=both) \
- $(call cc-ldoption, -Wl$(comma)--build-id) -Wl,-Bsymbolic $(LTO_CFLAGS)
+ $(call cc-ldoption, -Wl$(comma)--build-id) -Wl,-Bsymbolic
GCOV_PROFILE := n
#
diff --git a/include/linux/init.h b/include/linux/init.h
index 88646cb136e0..0370efacc839 100644
--- a/include/linux/init.h
+++ b/include/linux/init.h
@@ -157,23 +157,6 @@ extern bool initcall_debug;
#ifndef __ASSEMBLY__
-#ifdef CONFIG_LTO
-/* Work around a LTO gcc problem: when there is no reference to a variable
- * in a module it will be moved to the end of the program. This causes
- * reordering of initcalls which the kernel does not like.
- * Add a dummy reference function to avoid this. The function is
- * deleted by the linker.
- */
-#define LTO_REFERENCE_INITCALL(x) \
- ; /* yes this is needed */ \
- static __used __exit void *reference_##x(void) \
- { \
- return &x; \
- }
-#else
-#define LTO_REFERENCE_INITCALL(x)
-#endif
-
/* initcalls are now grouped by functionality into separate
* subsections. Ordering inside the subsections is determined
* by link order.
@@ -186,8 +169,7 @@ extern bool initcall_debug;
#define __define_initcall(fn, id) \
static initcall_t __initcall_##fn##id __used \
- __attribute__((__section__(".initcall" #id ".init"))) = fn; \
- LTO_REFERENCE_INITCALL(__initcall_##fn##id)
+ __attribute__((__section__(".initcall" #id ".init"))) = fn;
/*
* Early initcalls run before initializing SMP.
diff --git a/kernel/Makefile b/kernel/Makefile
index e2ec54e2b952..f80ce824bb4f 100644
--- a/kernel/Makefile
+++ b/kernel/Makefile
@@ -29,9 +29,6 @@ KCOV_INSTRUMENT_extable.o := n
KCOV_INSTRUMENT_kcov.o := n
KASAN_SANITIZE_kcov.o := n
-# cond_syscall is currently not LTO compatible
-CFLAGS_sys_ni.o = $(DISABLE_LTO)
-
obj-y += sched/
obj-y += locking/
obj-y += power/
diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index 11602e5efb3b..a5dd16ffb06e 100644
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -147,7 +147,7 @@ $(multi-objs-y:.o=.s) : modname = $(modname-multi)
$(multi-objs-y:.o=.lst) : modname = $(modname-multi)
quiet_cmd_cc_s_c = CC $(quiet_modtag) $@
-cmd_cc_s_c = $(CC) $(c_flags) $(DISABLE_LTO) -fverbose-asm -S -o $@ $<
+cmd_cc_s_c = $(CC) $(c_flags) -fverbose-asm -S -o $@ $<
$(obj)/%.s: $(src)/%.c FORCE
$(call if_changed_dep,cc_s_c)
--
2.8.4
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